better failure message for img2enc

Signed-off-by: rogerdpack <rogerpack2005@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/img2enc.c

@@ -78,7 +78,7 @@ static int write_packet(AVFormatContext *s, AVPacket *pkt)
         if (av_get_frame_filename(filename, sizeof(filename),
                                   img->path, img->img_number) < 0 && img->img_number > 1 && !img->updatefirst) {
             av_log(s, AV_LOG_ERROR,
-                   "Could not get frame filename number %d from pattern '%s'\n",
+                   "Could not get frame filename number %d from pattern '%s' (either set updatefirst or use a pattern like %03d within the filename pattern)\n",
                    img->img_number, img->path);
             return AVERROR(EINVAL);
         }